DESCRIPTION: (Adapted from Applicant's Abstract). The application proposes
to continue to explore, using a prospective study design, the associations
of specific biochemical factors with subsequent development and diagnosis of
prostate cancer. Blood samples to be used in this study were collected at
baseline in 1982 from 14,916 men in the ongoing Physicians Health Study.
The blood will be analyzed, using a matched, nested, case-control design to
evaluate hypotheses in three main areas: markers for early detection,
hormonal factors, and nutritional biochemical factors. For early detection,
the application posits that determination of plasma percent free PSA will
markedly improve the sensitivity and specificity of PSA, especially for
those with PSA values near the conventional level of "positive" (4.0 ng/ml).
The plan is to assess the value of prostate-specific membrane antigen (PSMA)
for early detection of metastatic disease. There are also plans to assay
hormone levels (testosterone, dihydrotestosterone, 3a-androstanediol
glucuronide, SHBG, estradiol) in plasma to relate these to prostate cancer
risk. Analysis of the impact of genetic variations in the genes coding for
the androgen receptor and 5-alpha-reductase (an important enzyme in androgen
metabolism) will add further knowledge about prostate cancer aetiology, and
will permit assessment of interactions with hormone levels. The major
nutritional hypotheses relate to possible protective effects of lycopene and
vitamin E, and possible adverse effects of specific fatty acids (especially
alpha-linolenic acid and trans-fatty acids). In addition, studies are
planned to explore interactions between the baseline carotenoid levels and
the beta-carotene intervention. Prostate cancer endpoints are routinely
documented as part of the trial follow-up, which is funded from other
sources. The blood samples are already available for analysis. Hence, the
proposed analysis will make efficient use of existing resources which
provide the basis for a prospective study of prostate cancer. About 1,234
cases are projected by the end of the grant period, yielding sufficient
statistical power for informative results.
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